[6673]71FL Series 80 Rack & Pinion Focuser Set Part # 6673 Description 71FL Series 80 Rack & Pinion Focuser Set Aperture 71mm Fluorite Focal length 400mm F-ratio 5.6 Lens configuration 2 elements in 2 groups Coating Fully-multi-coated Physical length 330mm Tube diameter 80mm Weight 1.3kg Filter 72mm (front hood) Parts included 2573, 7151, 7801, 9850 & 7504 Notes BORG rack & pinion focuser version. 2-inch opening & M57-thread.